1. Field of the Invention
The present invention relates generally to safety devices. More particularly, the invention concerns a wire rope pre-failure indicating device and method of using the same that can be installed at any location along a length of conventional wire rope that provides a pre-failure warning that the wire rope has been loaded beyond a specified magnitude.
2. Discussion of the Prior Art
Flexible wire rope of various sizes is commonly used in various types of industrial applications, including cranes and similar lifting equipment. Wire rope is also extensively used in automotive and aircraft running gear, in marine halyards and in various other types of mechanical control systems.
In many prior art applications, the flexible wire rope is exposed to wear and potential damage as a result of being threaded through various pulleys and sheave configurations and of being wrapped upon and unwrapped from storage drums.
Less flexible wire rope of various sizes is more often used in more static applications such as stays to support construction elements, crane booms, towers, telephone poles, construction masts, and marine rigging.
In virtually all of the prior art applications the wire rope is installed into the load path by one of two techniques. In one technique the wire rope is wrapped around a thimble with the free end of the wire rope clamped to itself using either a mechanical clamp or a lead lug that is crimped onto the wire rope with a crimping tool. The second technique typically involves the step of swaging a designed eye or clevis end fitting onto the wire rope by extruding a section of the fitting into the twisted strands of the wire rope using a hydraulic die.
When dynamic tension is applied to the wire rope during any of the aforementioned applications, the wire rope can become overstressed. If the overstressed condition of the wire rope is not promptly discovered and the situation promptly corrected, the overstressed wire rope will fail resulting in serious and, on occasion, catastrophic damage or injury. The thrust of the present invention is to solve this serious prior art problem by providing an easy-to-use, highly reliable wire rope pre-failure indicating device that can be installed at any location along a length of conventional wire rope of the type used in a common industrial application and will function to provide a pre-failure warning that the wire rope has been overstressed and that corrective action must be taken.
U.S. Pat. No. 5,466,082 issued to Sherar, which is directed to an in-line safety shackle for a cable system, is primarily directed to a safety device for use in the logging industry. The Sherar device comprises a first member adapted to engage a first cable, and a second member adapted to engage a second cable, wherein the second member releasibly inter-fits with the first member. At least one safety cable is provided for substantially permanently securing the first member to the second member. The device also comprises means releasibly connecting the first member to the second member, the means being provided with a pre-determined shear force sufficient to release the first member from the second member before the first or second cable breaks due to the dynamic tension placed on the cables. The Sherar patent also describes an in-line safety shackle device for a cable system that includes a first cable and a second cable comprising a first member adapted to releasibly engage the first cable. The first member includes a first cable shaft and a first shear pin shaft. The first member further includes at least one safety cable shaft for receiving a first end of a safety cable. The device further comprises a second member adapted to releasibly engage the second cable. The second member includes a second cable shaft and a second shear pin shaft, wherein the second member is adapted to releasibly inter-fit with the first member. The shear pin is provided with a designed shear strength which is less than the tensile force of the safety cable.
The prior art patent to Ellis, et al., U.S. Pat. No. 5,400,868, concerns a shock-load indicator for use with a safety cable, and more particularly to a shock-load indicator for use with retracting life line devices. The Ellis, et al., shock-load indicator comprises a casing surrounding a section of the cable, having severable top and bottom sections connected through a shearing means. The casing normally supports the weight of the user of the cable, and encloses a length of the cable such that, when the cable is extended as a result of the severance of the casing due to a fall induced shock-load, the top and bottom sections separate by a pre-determined distance indicating that the cable has been subjected to a shock-load.